Multistage compressor installation

ABSTRACT

A multistage compressor installation in which compression stages utilizing centrifugal compressors are independently driven by drivers that can be electric motors configured to be controlled by a speed controller. Intercoolers are located between stages to remove the heat of compression and the stages are connected such that outlets are located opposite to inlets of the compressors and conduits connecting the intercoolers to the stages are in an in-line relationship to inhibit the formation of pressure drops between stages. The conduits connecting the stages incorporate tapered transition sections configured such that flow velocity gradually decreases towards the intercooler and gradually increases from the intercooler to the next succeeding compression stage to further inhibit pressure drops.

FIELD OF THE INVENTION

The present invention relates to a multistage compressor installation inwhich independently driven compression stages utilizing centrifugalcompressors with intercoolers connected such that outlets are locatedopposite to inlets of the compressors and conduits connecting theintercoolers to the stages are in an in-line relationship to inhibit theformation of pressure drops between stages. More particularly, thepresent invention relates to such a compressor installation in which theconduits incorporate tapered transition sections configured such thatflow velocity gradually decreases towards the intercooler and graduallyincreases from the intercooler to the next succeeding compression stage.

BACKGROUND OF THE INVENTION

Gases are compressed in many different types of industrial facilitiesand for a variety of purposes. For example, air is compressed, cooledand introduced into one or more distillation columns in an airseparation plant. In a liquefier, a gas is compressed and sufficientlycooled to a liquid. There are many other examples of industrialfacilities in which gases are compressed.

In any facility, although a single compressor stage can be used tocompress the gas, more typically, the gas is compressed in multiple,sequential compressor stages. The reason for this is as the gas iscompressed, its temperature rises. The elevated gas temperature requiresan increase in power to compress the gas. In a typical compressorinstallation utilizing individual stages, each stage uses a centrifugalcompressor in which gases entering an inlet to the compressor aredistributed to a vaned compressor wheel that rotates to accelerate thegas and thereby impart the energy of rotation to the gas. This increasein energy is accompanied by an increase in velocity and a pressure rise.The pressure is recovered in a vaned or vaneless diffuser that surroundsthe compressor wheel and functions to decrease the velocity of the gasand thereby increase the gas pressure of the compressed gas. Thecompressed gas is discharged by a volute of spiral-like configurationthat terminates in an outlet of the compressor. The gas is thereforedischarged from the outlet at right angles to the incoming gas to becompressed.

Since the gas has been compressed, its temperature has also increased.The heated compressed gas is cooled between the compressor stages byintercoolers in which the heated compressed gas cools through indirectheat exchange with a coolant, for instance, air or water.

Typically, the multistage compressor installation described above isdriven by a common gearbox having an electric motor driving a bull gearthat in turn drives pinions that are connected to compressor shafts thatrotate the compressor wheels. Since the gas is gradually compressed fromstage to stage, each compressor pinion may rotate at a different speedand torque related to the pressure rise to be accomplished in aparticular stage on that pinion. This arrangement is particularlyadvantageous in an air separation plant in which it is desirable for acommon plant design to be utilized with different gearing arrangementsthat can be used to meet production requirements for a particular plant.Additionally, since an air separation plant requires refrigeration thatis generated by turboexpanders, the work of expansion can easily berecovered by gearing between the turboexpander and the bull gear. Thedisadvantage of such arrangement is that since the compression stagesare arranged around the bull gear, the piping or conduits connecting thestages to the intercoolers can become quite convoluted. Each bend in theconduits results in a pressure drop due to turbulence induced in theflow by the change in direction of the gas within the bend.Additionally, the conduits lead directly to the intercoolers, a rapidincrease in flow area results at the connection of the conduits to theintercooler. This rapid increase in flow area also results in a pressuredrop due to the resulting turbulence that is induced into the flow.Also, mal-distributions in flow can occur in the intercooler such thatnot all of the heat exchange passages are utilized effectively.

Another disadvantage of the arrangement discussed above is that thereare irreversible heat loses in gearboxes used in housing the bull gearand pinions. Further, since the torque is transmitted in a gearedarrangement, there are certain mechanical requirements for the size ofgear teeth resulting in limitations in the size of the pinions andtherefore, speed that can be induced in each of the compression stages.These limitations are overcome through utilization of variable speedelectric motors driving each of the compression stages individually. Anexample of this is shown in US Patent Application No. 2007/0189905 thatis specifically designed to overcome the limitations discussed directlyabove. However, in this patent application, there is no appreciation ofthe pressure drops that can be induced due to the connection of theintercoolers with the compression stages.

As will be discussed, the present invention provides a compressorinstallation utilizing centrifugal compressors and interstage cooling inwhich each of the compressors is independently driven and positioned ina manner that incorporates low pressure drop connections between thestages and to the intercoolers located between stages.

SUMMARY OF THE INVENTION

The present invention, in one aspect, provides a multistage compressorinstallation that comprises two compression stages to compress a gas andan intercooler positioned between the two compression stages to removeheat of compression from the gas between the two compression stages.Each of the two compression stages comprise a centrifugal compressor anda driver configured to independently drive the centrifugal compressor ofeach of the two compression stages, the centrifugal compressor having aninlet surrounded by a volute and the volute having an outlet oriented soas to discharge compressed gas at right angles to the inlet. An inletconduit connects the outlet of one of the two compression stages to theintercooler and an outlet conduit connects the intercooler to the inletof the other of the two compression stages. The outlet of the one of thetwo compression stages is located substantially opposite to the inlet ofthe other of the two compression stages such that the inlet conduit andthe outlet conduit are in an in-line relationship to inhibit pressuredrop in the inlet conduit and the outlet conduit. Further, each of theinlet conduit and the outlet conduit is provided with tapered transitionsections of ever increasing transverse cross-sectional area in the inletconduit and ever decreasing transverse cross-sectional area in theoutlet conduit such that flow velocity is gradually decreased in theinlet conduit and gradually increased in the outlet conduit to furtherinhibit pressure drops at connections between the inlet conduit and theintercooler and the outlet conduit and the intercooler.

In another aspect, the present invention provides a multistagecompressor installation that comprises a plurality of compressionstages, including at least four compression stages, to compress a gasand intercoolers positioned between the compression stages to removeheat of compression of the gas between compression stages. Each of thecompression stages comprise a centrifugal compressor and a driverconfigured to independently drive the centrifugal compressor of each ofthe compression stages. The centrifugal compressor has an inletsurrounded by a volute and the volute has an outlet oriented so as todischarge compressed gas at right angles to the inlet. Pairs of conduitsconnect the intercoolers to the compression stages. An after-cooler isconnected to a final of the compression stage and at least one of thepairs of the conduits sized longer than at least one other adjacent pairof the pairs of conduits and all of the compression stages, intercoolersand the after-cooler are substantially located in a common plane suchthat the compression stages, intercoolers and the after-cooler arearranged in a spiral-like configuration.

Alternatively, the compression stages can be arranged in a helical-likeconfiguration on at least two levels. The helical-like configuration canbe produced by orienting the volute of each of the compression stagessuch that the outlet is located above the inlet. In another alternative,four of the compression stages can be arranged in a vertical plane suchthat a second and a third of the compression stages are located above afirst and a forth of the compression stages, respectively.

Any of foregoing arrangements can be used without the tapered transitionsections connecting the compression stages to the intercoolers. However,each of the pairs of conduits can consist of an inlet conduit connectedto the outlet of the preceding stage and an outlet conduit connected tothe inlet of the following stage. The inlet conduit and the outletconduit can be provided with tapered transition sections of everincreasing transverse cross-sectional area in the inlet conduit and everdecreasing transverse cross-sectional area in the outlet conduit suchthat flow velocity is gradually decreased in the inlet conduit andgradually increased in the outlet conduit to further inhibit pressuredrops at connections between the inlet conduit and the intercooler andthe outlet conduit and the intercooler.

In any embodiment of the present invention, the intercooler can have abox-like housing that encloses passages for indirectly exchanging heatof compression from compressed gas produced in the one of the twocompression stages to a coolant circulating through the intercooler.Each of the tapered transition sections can be in the form of afour-sided polyhedron terminating in a rectangular transverse crosssection at the connections of the inlet conduit to the intercooler andthe outlet conduit and the intercooler

Additionally, in any embodiment of the present invention, the driver canbe an electric motor. Such electric motor can have a shaft directlycoupled to the compressor and the motor can be configured such thatspeed of the electric motor is able to be controlled by a speedcontroller. Such an electric motor can be a permanent magnet motor.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly pointing outthe subject matter that Applicants regard as their invention, it isbelieved that the invention will be better understood when taken inconnection with the accompanying drawings in which:

FIG. 1 is an enlarged perspective view of an embodiment of the presentinvention;

FIG. 2 is a sectional view of FIG. 1 taken along line 2-2 of FIG. 1;

FIG. 3 is a sectional view of FIG. 2 taken along line 3-3 of FIG. 2;

FIG. 4 is a perspective view of an alternative embodiment of the presentinvention;

FIG. 5 is a rear elevational view of FIG. 4; and

FIG. 6 is a perspective view of another alternative embodiment of thepresent invention.

Reference numbers having the same description have been repeated in theFigures to avoid repetition in the explanation thereof in the followingdiscussion.

DETAILED DESCRIPTION

With reference to FIG. 1, a compressor arrangement 1 in accordance withthe present invention is illustrated that is designed to compress a gasstream 10 and thereby produce a compressed gas stream 12. Gas stream 10is compressed in four compression stages 14, 16, 18 and 20 in theproduction of compressed gas stream 12.

Each of the four compression stages 14, 16, 18 and 20 is provided with acentrifugal compressor 22 of known design having an inlet 24, a volute26 and an outlet 28. Each compressor 22 may be different from oneanother in that they may each incorporate a design that is specificallyconfigured to produce the desired pressure rise and an aerodynamiceffect to achieve the maximum efficiency in a manner well known in theart. For example, each subsequent stage may actually be physicallysmaller due to the increase in the fluid density. As illustrated, eachoutlet 28 discharges compressed gas to the next succeeding stage atright angles to the inlet. For example, gas stream 10 enters inlet 24 ofcompression stage 14 and is discharged from the outlet 28 to the inlet24 of the next succeeding stage 16 at right angles to the inlet 24 ofcompression stage 14. Each of the compression stages 14, 16, 18 and 20is independently driven by a driver 30. Each drive 30 is preferably anelectric motor of permanent magnet design that is capable of beingcontrolled by a variable speed controller. Each stage 14, 16, 18 and 20is connected to a support 32 by threaded connectors, such as bolts. Eachsupport is in turn connected to a concrete slab 2.

It is to be noted that each of the compression stages 14, 16, 18 and 20can be designed in a manner well known in the art. For example, eachsuch stage is employed to increase the pressure of the gas stream 10 andas such, compression stage 14 is the first compression stage,compression stage 16 is the second compression stage, compression stage18 is the third compression stage and compression stage 20 is the forthcompression stage. The present invention encompasses compressorarrangements having at least two compression stages and also, greaterthan four of such compression stages. Each compression stage is designedfor the pressure rise and flow that is desired in a particular stage.More latitude in the design is given the designer given the fact thatpreferably the speed of a driver 30 can be independently controlled fora particular stage. Also, as indicated above, each driver can be anelectric motor and in particular, a permanent magnet motor directlycoupled to the compressor. This being said, fluidic drives having apump, fluid motors and steam turbines are possible substitutes for suchelectric motors. Additionally other types of electric motors arepossible, such as induction motors and in general, electric motors thatwould operate at a fixed speed and geared by a gearbox to the particularcompression stage. Such an arrangement would not, however, be preferredgiven the attendant irreversible losses in gearboxes and the reducedfreedom of design in the compression stage that would otherwise beobtainable with the use of a variable speed, permanent magnet motor thatcould incorporate magnetic bearings to reduce irreversible thermallosses in such a device.

Between the compression stages 14 and 16, an intercooler 34 ispositioned to remove the heat of compression produced by the compressionof the gas stream 10 by compression stage 14. Similarly, betweencompression stages 16 and 18, an intercooler 36 is positioned to removethe heat of compression produced by the compression of the gas stream 10by compression stage 16 and an intercooler 38 is provided betweencompression stages 18 and 20 to remove the heat of compression generatedby compression stage 18. An after-cooler 40 is provided aftercompression stage 20 to remove the heat of compression generated bycompression stage 20 and such after-cooler has the same design asintercoolers 34, 36 and 38. In this regard, other possibilities existfor the after-cooler, for example direct fluid contact devices thatwould not necessarily be configured in the same manner as after-cooler40. Additionally, the box-like configuration of each of the intercoolers34, 36 and 38 and the after-cooler 40 is illustrated for exemplarypurposes only in that other configuration are also possible for suchdevices, for example, cylinders. Each of the intercoolers 34, 36 and 38and after-cooler 40 are supported by supports 42 and 44 that are in turnconnected to the concrete slab 2.

Each of the intercoolers 34, 38 and 38 are connected between thecompression stages: 14, 16; 16, 18; and 18, 20, respectively by pairs ofinlet and outlet conduits 46 and 48. Conduits 46 and 48 for each of thestages may incorporate a design that is specific for a stage. Forexample, pipe sizes might be small in subsequent higher pressure stages.Each of the pairs of inlet and outlet conduits 46 and 48 is formed byinlet and outlet sections 50 and 52, respectively, and inlet and outlettransition sections 54 and 56. Each of the inlet section 50 is providedwith a circular transverse cross-section at its connection with anoutlet 28 and a rectangular transverse cross-section at its connectionwith an inlet transition section 54. Similarly, each outlet section 52has a rectangular transverse cross-section at its connection with anoutlet transition section 56 and a circular transverse cross-section atits connection with an inlet 24. The compression stages 14, 16, 18 and20 are positioned so that each outlet 26 is located opposite to an inlet24 of a compression stage. For example, outlet 28 of compression stage14 is located opposite to the inlet 24 of the next succeedingcompression stage 16. This allows the pair of inlet and outlet conduits46 and 48 to be in an in-line relationship or substantially an inlinerelationship to prevent pressure drops from being produced by bends andelbow sections of piping that would otherwise be found in the prior art.It is to be noted, that gas stream is introduced into the inlet 24 ofcompression stage 14 by a piping network used in the apparatus thatemploys the compression arrangement 1 of which a pipe 49 is illustrated.

In addition to the foregoing, pressure drops are also reduced byprovision of the inlet and outlet transition sections 54 and 56. Each ofthe inlet sections 54 is designed so that the transverse cross-sectionalarea thereof increases from the outlet 28 of compression stages 14, 16and 18 towards their respective associated intercoolers 34, 36 and 38 sothat, preferably, the transverse cross-sectional areas of the inletsections 54 at their connections to the intercoolers 34, 36 and 38 arematching. Each of the outlet sections 56 is designed so that thetransverse cross-section area thereof decreases from the intercoolers34, 36 and 38 towards the inlet 24 of their respective associatedcompression stages 16, 18 and 20. Again, preferably, the transversecross-sectional areas of the outlet section 56 at their connection tothe intercoolers 34, 36 and 38 are equal. In such manner, the velocityof the flow gradually decreases as the intercoolers 34, 36 and 38 areapproached and gradually increases as the inlet 24 of compression stages16, 18 and 20 are approached to prevent turbulence from being induced inthe flow of the compressed gas by an otherwise sudden increase ordecrease in the flow area upon the gas flowing into and from anintercooler 34, 36 and 38 or for that matter after-cooler 40. Althoughnot illustrated, the interiors of the inlet sections 54 and the outletsections 56 can be provided with vanes to further inhibit pressure lossdue to turbulent flow.

As mentioned previously, after-cooler 40 has the same conceptual designas intercoolers 34, 36 and 38. As such, it also is provided with pairsof inlet and outlet conduits 46 and 48, formed by inlet and outletsections 50 and 52, respectively, and inlet and outlet transitionsections 54 and 56 to prevent turbulence from being introduced into theflow of compressed gas. As such, the discussion above with respect tothe intercoolers 34, 36 and 38 is equally applicable to the after-cooler40 with respect to the inlet and outlet sections 46 and 48 and thetransition sections 54 and 56 is equally applicable.

With reference to FIG. 2, intercooler 38 is illustrated for exemplarypurposes. Intercoolers 34 and 36 and after-cooler 40 are of the samedesign and the following discussion is equally applicable to suchcomponents. Intercooler 38 is provided with a box-like housing 60.Coolant fluid, which would be water in case of compressed air as the gasto be compressed, is admitted into an inlet plenum 62 by way of aflanged inlet 64. Inlet plenum 62 is provided with baffles 66 and 68.Baffle 66 constrains the coolant fluid to flow through passages 70 inthe direction of arrowhead “A” and then into a reverse plenum 72 havinga baffle 74 to cause the flow to reverse direction and flow throughpassages 76. The flow reverses direction within inlet plenum 62 and thenflows through passages 78 and into reverse plenum 72 on the other sideof baffle 74. The flow then reverses direction again and flows intopassages 80 and into the inlet plenum due to baffle 68. The flow isdischarged from a flanged outlet 82 in a direction of arrowhead “B”.With additional reference to FIG. 3, the compressed gas flows incross-flow to the coolant fluid in a direction of arrowhead C intofinned passages 84 to indirectly exchange heat with the coolant fluidflowing in cross-flow. As is apparent from the Figures, intercooler 38can be fabricated from conventional brazed aluminum plate fin heatexchanger construction. In this regard, intercooler 38 is sealed at thetop and the bottoms by top and bottom plates 83 and 85, respectively.

As is apparent from FIGS. 1-3, it can be seen that inlet and outlettransition sections 54 and 56 are formed from a four sided polyhedronhaving a configuration similar to a frustum of a cone. In this regard,if the intercooler 34 were provided with a housing of cylindricalconfiguration instead of the illustrated box-like configuration, theinlet and outlet sections 54 and 56 would in fact be of conicalconfiguration having a circular transverse cross-section in place of therectangular cross-section utilized for inlet and outlet transitionsections 54 and 56 are of rectangular cross-section that matches thecross-section of the passages 84, the flow is able to be evenlydistributed to the passages 84 that solves mal-distribution problemsseen in prior art intercoolers in which there exists a sudden increasein cross-sectional area at the connection of the inlet and outlets tothe intercooler.

With reference again to FIG. 1, it can be seen that the pairs of inletand outlet conduits 46 and 48 between compression stages 18 and 20 isalso provided with elongated sections 86 and 88 so that the pairs ofinlet and outlet conduits 46 and 48 are sized longer than the pair ofinlet and outlet conduits 46 and 48 associated with compression stages14 and 16 and 16 and 18 and the after-cooler 40. This allows thecompressor arrangement 1 to be of spiral-like configuration so that theforth compression stage 20 is outwardly spaced from the first of thecompression stages 14 and the first compression stage does not interferewith the outlet conduit 48 associated with the after-cooler 40 and thepiping network used in the apparatus that employs the compressionarrangement 1 of which a pipe 90 is illustrated. This is necessary giventhe rectilinear configuration of the compressor arrangement 1. In thisregard, the elongated sections 86 and 88 could be placed between any ofthe two compression stages 14, 16; 16, 18; and 18, 20. Moreover, if morethan four compression stages were desired, the compression stages couldspiral around those illustrated in compressor arrangement 1.

Other configurations are possible. For instance with reference to FIGS.4 and 5, a multistage compressor installation 1′ is illustrated in whichthe compression stages are arranged in a helical configuration toprovide two or more levels of compression stages. In this regard, thegas stream 10 is compressed in compression stages 14, 16, 18 and 20 withinter-stage heat removal by means of intercoolers 34, 36 and 38 asillustrated and described with respect to FIG. 1. Additionally,compression stage 20 discharges compressed gas to intercooler 100 and inturn compression stage 92. In the embodiment shown in FIG. 1, it is tobe recalled that compression stage 20 discharged compressed gas toafter-cooler 40. Compressed gas is discharged from compression stage 92to intercooler 102 and then to compression stage 94 and after-cooler 104to produce a compressed gas stream 12′ that is discharged from a pipe 96at a higher pressure than compressed gas stream 12 produced inmultistage compression installation 1′. The description of compressionstages 92 and 94, intercoolers 100 and 102 and after-cooler 104 are thesame as set forth above for compression stages 14-20, intercoolers 34-38and after-cooler 40, respectively. Therefore, the reference numbers forthe individual elements have been deleted from FIGS. 4 and 5 for ease ofexplanation. The compression stages 92 and 94, however, would bedesigned for a specific pressure rise and flow rate contemplated forsuch stages.

With particular reference to FIG. 5, the helical configuration of themultistage compressor installation is produced by suitably orienting thevolutes 26 to be opposite to the inlets 24 and to produce a slight risein elevation of successive stages. For example, the volute 26 associatedwith compression stage 18 is oriented so that its associated outlet 28lies above the inlet 24 associated with such compression stage. In FIG.1, the volute 26 associated with compression stage 18 is mounted to itsassociated compressor 22 so as to be rotated 360° from its position inFIG. 4. The volutes 26 associated with all of the compression stages ofmultistage compressor installation 1′ are similarly mounted. As aresult, there is an increase in the height of compression stage 16 in anamount of equal to the distance between the inlet 24 and the outlet 28of the volute 26 since the inlet 24 is centrally located in each of thevolutes 24. The same holds true for all of the other compression stagesfollowing compression stage 16 such that compression stages 92 and 94are located above compression stages 14 and 16, respectively and aremounted by connection of supports 32′ onto supports 32 associated withthe compression stages 14 and 16. Put another way, the helicalconfiguration provided within compressor installation 1′ is produced byorienting the volutes 26 so that the outlets 28 are located above theinlets 24. Another possibility would be to orient the volutes 26 at aslight angle and if necessary, slightly increase the lengths of theinlet and outlet conduits around the helical configuration ofcompression stages. This might be necessary where the volutes have toosmall a diameter to produce the necessary rise in the height of thestages.

With reference to FIG. 6, a multistage compressor installation 1″ isillustrated in which a second and third compression stages 16 and 18 arelocated above a first and a fourth of the compression stages 14 and 20such that the compression stages 14, 16, 18 and 20 are all situated in aplane that is vertical from the horizontal. Again, since the inlet andoutlet conduits 46 and 47 and the intercoolers 34, 36 and 38 andafter-cooler 40 have been fully described above, reference numbersindicating the individual elements thereof have not been included inthis Figure since the same have been fully described above. This type ofconfiguration has a narrow footprint that might be necessary given otherequipment of a facility that employs multistage compressor installation1″. As could be appreciated additional stages could be supplied alongside the four illustrated compression stages by utilizing theafter-cooler 40 as an intercooler oriented at right angles to the planeand then orienting other compression stages in another parallel verticalplane. The mounting for compression stage 14 and after-cooler 40 on theconcrete slab 3 by way of supports 22 and 42 and 44, respectively. Theother stages are mounted by means of supports 106 and 108 connected tointercooler 36. Supports 106 and 108 are connected by cross members 110and 112. It is to be noted that compression stages 16, 18 and 20 couldalso be mounted on a wall adjacent to the concrete slab 3 by individualsupporting elements.

It is to be noted that the multistage compressor installations 1, 1′ and1″ might be employed without the inlet and outlet conduits 46 and 48having the respective transition sections 54 and 56. However, as couldbe appreciated, the pressure drop and therefore the energy consumptionof such a facility would be greater in such installations.

While the present invention has been described with reference topreferred embodiments, as could be appreciated by those skilled in theart that numerous changes and omissions could be made without departingfrom the spirit and scope of the inventions as set forth in the appendedclaims.

1. A multistage compressor installation comprising: two compressionstages to compress a gas and an intercooler positioned between the twocompression stages to remove heat of compression from the gas betweenthe two compression stages; each of the two compression stagescomprising a centrifugal compressor and a driver configured toindependently drive the centrifugal compressor of each of the twocompression stages, the centrifugal compressor having an inletsurrounded by a volute and the volute having an outlet oriented so as todischarge compressed gas at right angles to the inlet; an inlet conduitconnecting the outlet of one of the two compression stages to theintercooler; an outlet conduit connecting the intercooler to the inletof the other of the two compression stages; the outlet of the one of thetwo compression stages located substantially opposite to the inlet ofthe other of the two compression stages such that the inlet conduit andthe outlet conduit are in an in-line relationship to inhibit pressuredrop in the inlet conduit and the outlet conduit; and each of the inletconduit and the outlet conduit having tapered transition sections ofever increasing transverse cross-sectional area in the inlet conduit andever decreasing transverse cross-sectional area in the outlet conduitsuch that flow velocity is gradually decreased in the inlet conduit andgradually increased in the outlet conduit to further inhibit pressuredrops at connections between the inlet conduit and the intercooler andthe outlet conduit and the intercooler.
 2. The multistage compressorinstallation of claim 1, wherein: the intercooler has a box-like housingenclosing passages for indirectly exchanging heat of compression fromcompressed gas produced in the one of the two compression stages to acoolant circulating through the intercooler; and each of the taperedtransition sections is a four-sided polyhedron terminating in arectangular transverse cross section at the connections of the inletconduit to the intercooler and the outlet conduit and the intercooler.For high pressure application more likely to be a cone.
 3. Themultistage compressor installation of claim 1, wherein the driver is anelectric motor.
 4. The multistage compressor installation of claim 3,wherein the electric motor has a shaft directly coupled to thecompressor and is configured such that speed of the electric motor isable to be controlled by a speed controller.
 5. The multistagecompressor installation of claim 4, wherein the electric motor is apermanent magnet motor.
 6. A multistage compressor installationcomprising: a plurality of compression stages, including at least fourcompression stages, to compress a gas and intercoolers positionedbetween the compression stages to remove heat of compression of the gasbetween compression stages; each of the compression stages comprising acentrifugal compressor and a driver configured to independently drivethe centrifugal compressor of each of the two compression stages, thecentrifugal compressor having an inlet surrounded by a volute and thevolute having an outlet oriented so as to discharge compressed gas atright angles to the inlet; pairs of conduits connecting the intercoolersto the compression stages; the compression stages, the intercoolers andthe pairs of conduits arranged such that the inlet of a successive stageof the compression stages is located opposite to the outlet of apreceding stage of the compression stages and the conduits of each ofthe pair of the conduits are substantially in an in-line relationship toinhibit pressure drops in the conduits; an after-cooler connected to afinal of the compression stage; and at least one of the pairs of theconduits sized longer than at least one other adjacent pair of the pairsof conduits and all of the compression stages, intercoolers and theafter-cooler are substantially located in a common plane such that thecompression stages, intercoolers and the after-cooler are arranged in aspiral-like configuration.
 7. A multistage compressor installationcomprising: a plurality of compression stages, including at least fourcompression stages, to compress a gas and intercoolers positionedbetween the compression stages to remove heat of compression of the gasbetween compression stages; each of the compression stages comprising acentrifugal compressor and a driver configured to independently drivethe centrifugal compressor of each of the two compression stages, thecentrifugal compressor having an inlet surrounded by a volute and thevolute having an outlet oriented so as to discharge compressed gas atright angles to the inlet; pairs of conduits connecting the intercoolersto the compression stages; the compression stages, the intercoolers andthe pairs of conduits arranged such that the inlet of a successive stageof the compression stages is located opposite to the outlet of apreceding stage of the compression stages and the conduits of each ofthe pair of the conduits are substantially in an in-line relationship toinhibit pressure drops in the conduits; and the compression stagesarranged in a helical-like configuration on at least two levels.
 8. Themultistage compressor installation of claim 7, wherein the helical-likeconfiguration is produced by orienting the volute of each of thecompression stages such that the outlet is located above the inlet.
 9. Amultistage compressor installation comprising: a plurality ofcompression stages, including at least four compression stages, tocompress a gas and intercoolers positioned between the compressionstages to remove heat of compression of the gas between compressionstages; each of the compression stages comprising a centrifugalcompressor and a driver configured to independently drive thecentrifugal compressor of each of the two compression stages, thecentrifugal compressor having an inlet surrounded by a volute and thevolute having an outlet oriented so as to discharge compressed gas atright angles to the inlet; pairs of conduits connecting the intercoolersto the compression stages; the compression stages, the intercoolers andthe pairs of conduits arranged such that the inlet of a successive stageof the compression stages is located opposite to the outlet of apreceding stage of the compression stages and the conduits of each ofthe pair of the conduits are substantially in an in-line relationship toinhibit pressure drops in the conduits; and four of the compressionstages arranged in a vertical plane such that a second and a third ofthe compression stages are located above a first and a forth of thecompression stages, respectively.
 10. The multistage compressioninstallation of claim 6 or claim 7 or claim 8 or claim 9, wherein eachof the pairs of conduits consist of an inlet conduit connected to theoutlet of the preceding stage and an outlet conduit connected to theinlet of the following stage and the inlet conduit and the outletconduit having tapered transition sections of ever increasing transversecross-sectional area in the inlet conduit and ever decreasing transversecross-sectional area in the outlet conduit such that flow velocity isgradually decreased in the inlet conduit and gradually increased in theoutlet conduit to further inhibit pressure drops at connections betweenthe inlet conduit and the intercooler and the outlet conduit and theintercooler.
 11. The multistage compressor installation of claim 10,wherein: each of the intercoolers has a box-like housing enclosingpassages for indirectly exchanging heat of compression from compressedgas produced in the one of the two compression stages to a coolantcirculating through the intercooler; and each of the tapered transitionsections is a four-sided polyhedron terminating in a rectangulartransverse cross section at the connections of the inlet conduit to theintercooler and the outlet conduit and the intercooler.
 12. Themultistage compressor installation of claim 10, wherein the driver is anelectric motor.
 13. The multistage compressor installation of claim 12,wherein the electric motor has a shaft directly coupled to thecompressor and is configured such that speed of the electric motor isable to be controlled by a speed controller.
 14. The multistagecompressor installation of claim 13, wherein the electric motor is apermanent magnet motor.